At present, notification of an event, such as an incoming call, to a user in a mobile phone generally is carried out by way of, for example: presentation by a sound such as a ring alert or a ring melody; presentation by vibration such as a vibration alert; or presentation by light such as lighting of an LED lamp. Event notification by the presentation of a sound or vibration as described above has a problem in that sudden generation of a sound or vibration may give a shock or a sense of discomfort to a user.
In order to solve this problem, the following methods have been proposed: a method in which a sound notifying an incoming call is increased gradually with time (see Patent Document 1, for example); a method in which vibration notifying an incoming call is increased gradually (see Patent Document 2, for example); and methods in which the above-described methods are used in combination (see Patent Documents 3 and 4, for example). Also, there has been proposed a method in which a device for notifying an event is placed on a wrist or the like of a user, and a low-frequency electrical stimulus is given to a human body (user) by this device (see Patent Document 5). The above-described method in which a sound notifying an incoming call is increased gradually with time is referred to as “Ramped Ringer”.